Micromirrors and micromirror arrays can be used in a variety of applications. As an example, as individual devices, micromirrors can be applied to endoscopic optical imaging applications as the optical scan engine for various imaging modalities including, but not limited to Confocal Laser Scanning Microscope (CLSM), Non-linear Optical Microscope (NLOM), and Optical Coherence Tomography (OCT). Further, as an array of devices, micromirror arrays can be used as an optical phased array (OPA) for laser detection and ranging applications, such as those utilized in national defense and homeland security. Preferably, for use in OPAs, the micromirror arrays should generate tip/tilt and piston (TTP) motions.
Micromirror arrays can also be used as a wave front correction device in adaptive optics systems. In addition, micromirror arrays can play an important role in aerospace exploration and astronomy studies.
In the above mentioned applications, such as when being used as the optical scan engine for an endoscope, micromirrors having a high fill factor and, in particular, those having a small device footprint and large optical aperture, are desired.
The device footprint of a micromirror is determined, in large part, by its form factor. For micromirror arrays, the fill factor also strongly impacts the coupling efficiency, resolution, and speed of the micromirror array. As mentioned above, in many applications, a high fill factor is desired.
Existing high-fill-factor (HFF) micromirror/micromirror arrays are typically based on electrostatic actuation or electrothermal actuation. Currently, there are two types of HFF electrostatic micromirror/micromirror arrays. The first type is formed through thin film micromachining technology. The second type is formed through bulk silicon micromachining technology. HFF electrostatic micromirror/micromirror arrays based on thin-film MEMS process (e.g., MUMPs and SUMMiT-V) commonly only produce small-aperture-size mirrors, and therefore are not typically suitable for optical imaging. This is because as optical imaging requires large apertures to obtain high resolution. HFF electrostatic micromirror/micromirror arrays with bulk silicon mirror plates can provide large optical apertures. However, HFF micromirror/micromirror arrays with bulk silicon plates commonly require either dedicated bonding steps for mirror plate transfer or a specially designed substrate, making the fabrication processes complicated and expensive.
Existing electrothermal actuation micromirror/micromirror arrays utilize flip chip bonding for mirror plate transfer. For example, a HFF electrothermal micromirror array with a bulk silicon mirror plate was also reported, but it requires flip-chip bonding process for mirror plate transfer and has limited degrees of freedom. “Flip-Chip Integrated SOI-CMOS-MEMS Fabrication Technology,” by P. J. Gilgunn and G. K. Fedder, (Hilton Head Solid-State Sensors, Actuators and Microsystem Workshop, pp. 10-13 (June 2008)).
Other common drawbacks of both electrostatic and electrothermal HFF micromirror arrays include that the mirror plates do not have mechanical protection and the arrays need dedicated packaging steps for the devices to be ready to use.